1. Field of the Invention
The invention relates to a gas turbine, comprising a device for the fuel injection, which injects fuel into a mixing device, the injected fuel being mixed with combustion air in the mixing device. The gas turbine also has a combustion chamber arranged downstream of the mixing device, the length of the combustion chamber being L.sub.BK and the length of the mixing device being L.sub.Mix.
2. Discussion of Background
Undesirable thermoacoustic vibrations often occur in combustion chambers of gas turbines. In this case, thermoacoustic vibrations denote thermal and acoustic disturbances which amplify one another. In the process, high vibration amplitudes may occur and these may lead to undesirable effects, such as, for instance, high mechanical loading of the combustion chamber, increased emissions due to inhomogeneous combustion, and even extinction of the flame.
The cooling air which flows into the combustion chamber has an important function in the case of conventional combustion chambers, since the cooling-air film on the combustion-chamber wall has a sound-damping effect. In modern gas turbines, however, virtually the entire portion of the air is directed through the burner itself in order to achieve the lowest possible NO.sub.x emissions, and therefore the portion for the film cooling of the combustion chamber is reduced. As a result, the cooling air largely does not function as a damper of acoustic and thermoacoustic vibrations.
A further possibility of sound damping consists in coupling Helmholtz dampers in the region of the cooling-air feed, as described, for instance, in EP-A10576717. However, this is not always possible for reasons of space. In addition, this method often requires considerable expenditure in terms of design.